<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Document</title>
</head>
<body>
    <script>
        //underfined
        var x;
        //alert(x)
        console.log(x)
        var str1 = "hello word";
        var str2 = 'hello word';
        console.log(str1);
        console.log(str2);
        var str3 ='小明说;"小红真漂亮"'
        console.log(str3);
        //字符串替换
        var str= "Java";
        //1.下面代码执行顺序 限执行等号右侧代码 然后赋值给左边变量
        //2.JS字符串的加法时拼接字符串
        str = str+ "Script";//放到左侧str过程中str中Java被删掉 新的javasc放入
        console.log(str);
    </script>
</body>
</html>